1. Field of the Invention
The present invention relates to a fuel cell system including at least one fuel cell stack and at least one Venturi pump.
2. Description of the Related Art
In a contemporary fuel cell system, concentrated fuel and pure water are mixed to a fuel mixture. For this purpose, water and fuel flow into a mixer. Fuel and water are mixed and stored in the mixer. The mixture of fuel and water flows through an outlet of the mixer to a fuel cell stack.
The structure of a fuel cell system disclosed in U.S. 20040166389 and U.S. 20040062964 is shown in FIG. 1. Direct methanol fuel cell (DMFC) stack 10 comprises cathode air inlet 11 and cathode air outlet 13. Air pump 12 supplies reaction air to a cathode of fuel cell stack 10 through cathode air inlet 11. DMFC fuel cell stack 10 is supplied with a fuel stream that includes water and methanol on an anode side, and is supplied with an oxidant stream (air or oxygen) on a cathode side.
DMFC fuel cell stack 10 directly produces electricity through electrochemical reaction. Membrane 14 of DMFC fuel cell stack 10, which is disposed between the anode side and cathode side, is permeable to water, and thus during an operation of DMFC fuel cell stack 10, water is transferred from the anode side to the cathode side due to electro-osmotic drag. Heat exchanger 50 cools exhaust outputted from cathode outlet 13 by the use of cooling air 51. The exhaust from cathode outlet 13 may include steam (water). When the steam flows through heat exchanger 50, the steam is condensed and becomes water. The water flows to water separator 60 from heat exchanger outlet 52. The water is separated in water separator 60 from other substances (or air), and is injected into main anode circuit 18. Main anode circuit 18 is a passage that is connected to the anode side of stack 10. Air exits water separator 60 through venting opening 61. Liquid outlet 62 of water separator 60 is connected to main anode circuit 18.
An anode fuel circuit, which is formed through main anode circuit 18, includes circulation pump 23 that feeds a fuel mixture to stack anode inlet 15, carbon dioxide separator 20 connected to stack anode outlet 16, and mixer 40 that mixes a concentrated fuel from tank 30 with water recovered from heat exchanger 50. The concentrated fuel is supplied to mixer 40 through fuel connection 32, and the water is supplied to mixer 40 through water connection 64. Fuel pump 31 pumps the fuel into mixer 40 from tank 30, and water recovery pump 63 causes the water to flow into mixer 40. Carbon dioxide separator 20 includes carbon dioxide separator gas outlet 21 and liquid outlet 22. Carbon dioxide separator 20 separates liquid from the exhaust outputted from anode outlet 16. The liquid may include fuel or water.
A device combining the functions of a carbon dioxide separator, a water separator, a mixer, and a tank is described in EP 1 383 190 A1 and EP 1 383 191 A1. The structure of the device is shown in FIG. 2. Inlet for a stream of water/air 101 is located on the top part of the device. Water 106 is separated from air by gravity, and falls to the bottom of the device. Inlet stream of fuel 102 is located at the bottom of the device which works as a liquid hold-up tank. In the liquid hold-up tank, fuel and water are mixed. The gas from the incoming stream exits the device through outlet vent 104 which has a membrane that blocks penetration of liquid but allows penetration of gas. Liquid mixture exits the device through outlet 103 and flows to a fuel cell stack.
Regarding the combination of the function of the mixer and the tank, the problem is that the proper operation of the device depends on the orientation of the device. Therefore, if the device is used in a portable system, the portable system should be stayed in one position or in a fixed orientation. The device disclosed in EP 1 383 190 A1 and EP 1 383 191 A1 works only in an upright position, and does not properly work in a tilted position. Otherwise, the device would require additional safety installations protecting the device against dysfunction. Another problem is that the device has a significantly large volume and large height, because the device is a combination of the carbon dioxide separator, the water separator, the mixer, and the tank. The large volume of the device make it difficult to integrate the DMFC system in a laptop docking station or in a battery-like system.
Additionally, a pump feeding a fluid into a main circuit is necessary, but is not suitable because the use of the pump increases the complexity, volume, and weight of the system, while degrading the system efficiency due to the requirement of additional energy for the operation of the pump.